3-Hydroxy fatty acids (3-OH-FAs) are biomarkers for Gram-negative bacteria. Recent research has suggested that they could serve as temperature proxies in both terrestrial and marine environments, based on calibrations using modern samples. However, these proxies have been only applied in a speleothem for the Holocene and a short sediment core in the East China Sea for past 58 years, thus more evidence is needed to testify their validity. In this study, we analyzed the distribution of 3-OH-FAs in a sediment core from the northern South China Sea (SCS) spanning the past 19 thousand years (19 ka). We detected 3-OH-FAs, including normal (-), iso (-), and anteiso (-) isomers, in all 56 samples with carbon numbers ranging from 10 to 18. The distribution of 3-OH-FAs in marine sediments differed from that in terrestrial sediments (soil, stalagmite, and lake sediments), with a higher fractional abundance of anteiso-FAs. Two temperature proxies, RANs and RAN, showed a positive correlation (R = 0.5; < 0.001), with RANs-SST being closer to the actual sea surface temperature (SST). The reconstructed RANs-SST in our core exhibited a typical glacial-Holocene increase of 2–3 °C (20.8 ± 2.7 °C vs. 24.1 ± 1.3 °C). Several abrupt climate events, such as the Younger Dryas, BØlling/AllerØd, and Heinrich Event 1, were also recorded in RANs-SST. Therefore, our study supports the applicability of 3-OH-FA RANs as a temperature proxy for paleoenvironmental reconstructions, at least in the last glacial periods.

中文翻译：

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末次冰消期以来南海3-羟基脂肪酸的分布：基于3-羟基脂肪酸的古温度测量法的适用性

3-羟基脂肪酸 (3-OH-FA) 是革兰氏阴性菌的生物标志物。最近的研究表明，根据使用现代样本的校准，它们可以作为陆地和海洋环境中的温度代理。然而，在过去的58年里，这些代理仅应用于全新世的洞穴和东海的短沉积岩芯，因此需要更多的证据来证明其有效性。在这项研究中，我们分析了过去 19000 年（19ka）南海北部（SCS）沉积物岩心中 3-OH-FA 的分布。我们在所有 56 个碳原子数为 10 至 18 的样品中检测到了 3-OH-FA，包括正 (-)、异 (-) 和反异 (-) 异构体。 3-OH-FA 在海洋沉积物中的分布与陆地沉积物（土壤、石笋和湖泊沉积物）不同，antiso-FAs 的丰度分数更高。两个温度代理 RAN 和 RAN 显示出正相关性（R = 0.5；< 0.001），其中 RANs-SST 更接近实际海面温度 (SST)。我们的核心重建的 RANs-SST 显示出典型的冰川-全新世温度升高 2-3 °C（20.8 ± 2.7 °C 与 24.1 ± 1.3 °C）。 RANs-SST 中还记录了一些突发气候事件，例如新仙女木期、BØlling/AllerØd 和海因里希事件 1。因此，我们的研究支持 3-OH-FA RAN 作为古环境重建的温度代理的适用性，至少在末次冰河期是这样。